Light responsive electrical lamp dimming circuit



United States Patent US. Cl. 315-149 8 Claims ABSTRACT OF THE DISCLOSURE A light responsive electrical lamp dimming circuit is shown which is adapted for simultaneously controlling the intensity level of a plurality of lamps connected in parallel across an alternating current voltage source. In one embodiment, a light responsive trafiic signal lamp dimming system is used with a traffic signal controller to abruptly and simultaneously dim the traflic signal lamps of the traffic signal faces of at least one phase or all of the traflic signal lamps of the entire intersection from a high intensity level to a predetermined low intensity level when the background illumination is less than a preselected level. The light responsive dimming circuit disclosed herein includes a unilaterally conducting means controlled by a switching means, such as a relay, which in turn is controlled by a light sensing means, such as for example a photocell, which senses the background illumination.

Electrical lamp dimming circuits which selectively switch a rectifier into and out of a circuit for changing the intensity of a lamp are known; see for example, Patent Nos. 2,896,125; 3,009,071; 3,028,525 and 3,037,146. In such electrical lamp dimming circuits, the rectifier, when connected into the energizing circuit, causes the lamp to operate at a preselected minimum intensity level. When the rectifier is selectively switched ut of the circuit, the lamp is permitted to be energized by the energizing circuit at a normal intensity. Thus, by manually switching the rectifier into and out of the energizing circuit, the lamp intensity is abruptly changed 'between one of two discrete intensity levels.

The electrical lamp switching mechanism disclosed in Patent No. 2,896,125 is typical. In Patent No. 2,896,125 a bypass circuit is connected in parallel to the rectifier. The bypass circuit includes a switching mechanism having a switching member which, when manually connected in parallel to the rectifier, enables the energizing circuit to apply normal voltage to the lamp thereby operating the lamp at a normal intensity level. When the switching member is manually switched to an open-circuit position, the rectifier is rendered conductive for approximately one-half of an alternating current voltage cycle. The lamp is then abruptly dimmed to a lower intensity level which is equal to about one-third of the normal intensity level relative to the normal intensity level when the lamp is operated at normal voltage.

Another known system for selectively dimming the lumen output of an electrical lamp is shown in Patent No. 3,061,744. The lamp dimming circuit utilizes a fourlayer diode, such as a Zener diode, in combination with a half-wave rectifier connected in a back-to-back relationship. Such a combination permits manual control of the voltage applied to a lamp such that the lumen output thereof can be selectively varied from substantially zero percent to 100 percent.

In addition to the above, Patent No. 3,061,744 also discloses circuitry for triggering the gate of a siliconcontrolled rectifier (SCR). Also, this circuitry includes switching means for selectively switching a diode into ice and out of parallel relationship with the silicon-controlled rectifier in order to dim the lumen output of the lamp over a range of between zero and percent.

Use of SCRs as a continuously variable dimmer switch for controlling the intensity level of a lamp at a manuallyset intensity level is disclosed in US. Patent Nos. Re. 26,119 and 3,103,618. For example, in Patent No. 3,103,618, a variable phase shift circuit is used to provide a controllable gating signal for the gate electrode of the SCR in response to a manual setting of a variable resistor in the phase control circuit.

Light responsive switching circuits for selectively energizing and de-energizing a lamp as a function of ambient light illumination are known in the art. For example, in Patent Nos. 3,088,051 and 3,210,611, a light responsive element is used to control actuation of a relay by means of a transistor switching circuit for selectively energizing a lamp. In the circuits in each of the Patent Nos. 3,088,051 and 3,210,611, the lamps are abruptly switched between two different levels of illumination; namely substantially 100 percent lumen output when the lamps are energized and zero percent lumen output when the lamps are deenergized.

One primary disadvantage of the prior art devices, including those discussed hereina'bove, resides in that a light sensing means heretofore has been used for selectively actuating and deactuating a lamp in response to ambient illumination levels in the vicinity of the light sensing means. Further, the electrical lamp dimming circuits of the prior art, including those cited above, can be selectively controlled only in response to a manual setting of a dial or its equivalent.

The present invention overcomes the disadvantage of the prior art devices, including those set forth above, by a unique light responsive electrical lamp dimming system and means which abruptly and simultaneously changes the intensity of a plurality of lamps connected in parallel across an alternating current source between a high intensity level and a predetermined low intensity level when the background illumination in the vicinity of the lamps is less than a preselected level.

The prior art devices which utilize a light sensing means have apparently neither recognized the advantage of nor solved the problem of abruptly dimming the intensity of all the traffic signal lamps at an intersection in response to the background illumination. In the embodiment disclosed herein, the background illumination impinges on a light sensing means, such as for example a photocell.

One important use of a light responsive electrical lamp dimming means of the present invention is in a traffic control system. One problem encountered by traflic control engineers in designing traffic signal systems is to match the intensity level or lumen output of a trafiic signal lamp at a level which is compatible with the background illumination at on intersection served by the traflic lighting system. For example, around sunset on a rela tively clear day, a driver travelling in a westerly direction normally has the sun directly in his eyes. When a driver travelling in a westerly direction on such a day approaches a trafiic signal section having a setting sun directly therebehind as the background illumination, he may not be able to distinguish which trafiic condition is being displayed by the trafiic signal lamp servicing the lane in which he is travelling. One reason why a driver cannot sometimes distinguish the signal condition for his lane is that the traffic signal lamp has an intensity level which is equal to or lower than the intensity level of background illumination; namely, the setting sun.

One way of solving a problem presented by a setting sun as described above is to utilize a traflic signal lamp having a high intensity level or lumen output. This would require increasing the intensity level of the lamp such that it is substantially brighter relative to the background illumination, e.g. the setting sun, than the intensity level of the lamp when the background illumination is dark. After the sun has set, the background illumination is substantially reduced in level. The background illumination may be a dark sky or could be derived from artificial lighting, such as for example fluorescent signs, overhead street light and the like. In either case, if the traffic signal lamp intensity was increased so as to be brighter to compensate for the background illumination including the setting sun, the lamp would be extremely bright in a dark background illumination. A driver approaching an intersection under such a condition could be blinded by the bright or high intensity traffic signal lamp.

The advantages and desirability of controlling the intensity of the traffic signal lamp such that its intensity is at a high level when the background illumination in the vicinity of the lamp is at a bright level and its intensity is at a lower level when the background illumination is at a lower level is readily apparent.

Many attempts have been made, without a great deal of success, to match or correlate the intensity of a traffic signal lamp with its associated background illumination. At intersections where the sky and other background illumination are at a relatively normal level during the day and are at a dark level after sunset, trafiic signal lamps are used which have a wattage rating less than that required by traffic highway standards. A lower wattage traffic signal lamp having a dark background illumination is not apt to blind a motorist travelling in a vehicle toward the intersection being serviced by the traffic signalling system.

Another prior art solution to this problem has been to utilize a transformer having a normal voltage winding and a separate bucking winding for supplying voltages to the trafiic signal lamp. When a reduced voltage is required, the bucking winding is energized which in turn generates an opposite magnetic field which results in a reduced voltage being applied to the trafiic signal lamps. The reduced voltage, in turn, operates the lamps at a reduced intensity level. Use of transformers with separate bucking windings results in a traffic signal light dimming circuit having several disadvantages, such as for example being relatively expensive, being limited in range of control, being bulky and heavy and being difficult to install in existing trafiic signal sections.

One advantage of the present invention is that a unique and relatively inexpensive light responsive electrical lamp dimming means is provided which is capable of abruptly and simultaneously dimming the traffic signal lamps in all of the traffic signal heads of a single phase. The intensity of the traffic signal lamps can be abruptly changed from .a high intensity level to a predetermined low intensity level when the background illumination is less than a preselected level.

Another advantage of the present invention is that more than one phase but less than all of the phases can have the traffic signal lamps of the traffic signal heads therein abruptly and simultaneously dimmed.

Yet another advantage of the present invention is that all of the traffic signal lamps in all of the traffic signal faces in every phase at an intersection can be abruptly and simultaneously dimmed.

Another advantage of the present invention is that side glow can be effectively reduced and controlled from a display device adapted for use as a traffic signal section. One such display device includes a condensing display lens defining a viewing surface, lighting means for providing modifiable diffuse illumination of the lens from points substatnially at the focus of the lens and aperture means disposed substantially at the focus which outlines a predetermined viewing area, such as for example a selected traffic lane, as described in a copending patent application of Roger H. Appeldorn, Ser. No. 571,639, having a common assignee. Normally, such side glow is a function of the intensity of the traific signal lamp and is most noticeable when the traffic signal lamp intensity is substantially greater than the intensity of the background illumination. Thus, dimming of the traffic signal lamp is when the sensed background illumination less than a preselected level is eifective to reduce and control such side glow.

Another advantage of the present invention is that the intensity of the trafiic signal lamps in all of the traffic signal heads at the entire intersection can be abruptly changed between the high intensity level and the predetermined low intensity level for other unusual background conditions. For example, the entire intersection may have a background illumination which is at a low level during daylight hours such that the intensity of the trafiic signal lamps should be at an intensity level which is less than normal. The same intersection could well have a background illumination which is at a brighter level during nighttime hours than daytime hours. Such a brighter background illumination level could be due to artificial street lighting, neon signs and the like. In this instance, the intensity of the trafiic signal lamps in the entire intersection would then be increased in intensity to compensate for the brighter background illumination.

These and other advantages of the present invention will become apparent when considered in light of the descripiion of several embodiments set forth herein taken together with the drawing wherein:

FIGURE 1 is a diagrammatic representation, partially in block and schematic diagram, illustrating a light responsive electrical lamp dimming circuit and system adapted for use with a traffic signalling system controlling traffic fiow through an intersection; and

FIGURE 2 is a schematic diagram, partially in block form, of another embodiment of a light responsive electrical lamp dimming system which can be used in lieu of that of FIGURE 1.

Briefly, this invention relates to a light responsive electrical lamp dimming circuit and system adapted for abruptly and simultaneously changing the intensity level of trafiic signal lamps in a trafiic signal control system between a high intensity level and a predetermined low intensity level. The dimming circuit or system is adapted to control the intensity of traffic signal lamps of all of the traffic signal faces in at least one phase or of all of the traffic signal lamps of an entire intersection.

In one embodiment, the light responsive traffic signal lamp dimming circuit includes a unilaterally conducting means adapted to be electrically connected between the common neutrals of traffic signal faces, of the phase or phases in which the traffic signal lamps are to be dimmed, and system ground and in a direction to be conductive for approximately one-half of the alternating current voltage cycle. A switching means including a switchable circuit device having a first conduction state and a second conduction state is electrically connected in parallel to the unilaterally conducting means. The switching circuit device when in its conduction state bvpasses the unilaterally conducting means for connecting the lamps across the alternatirig current voltage source to operate the lamps at the high intensity level. The switchable circuit device when in its second conduction state enables the unilateral conducting means to be rendered conductive for connecting the lamps across the alternating current voltage source for approximately one-half of the alternating current voltage cycle to operate the lamp at the predetermined low intensity level. A control means having a first control state and a second control state is operatively connected to the switchable circuit device for changing the switchable control device from the first conduction state to a second conduction state. When the control means is in the first control state, the switchable circuit device is in the first conduction state. When the control means is in the second control state, the switchable circuit device changes from its first conduction state to a second conduction state. A light sensing means electrically con nected to the control means senses the background illumination and changes the control means from the first control state to the second control state when the sensed background illumination is less than a preselected level to change the switchable circuit device from the first conduction state to a second conduction state to abruptly and simultaneously change the intensity level of the lamp in the trafiic signal face of the phase or phases from the high intensity level to the low intensity level while the sensed background illumination is less than the preselected level.

FIGURE 1 illustrates diagrammatically a typical intersection of two highways, generally designated by dashed lines 12 and 14, which are serviced by a traffic signal system. The traflic signalling system illustrated herein for purposes of example comprises four traflic signal faces designated 16, 18, 20, 22 and a traffic signal controller 24. The trafiic signal controller 24 is electrically connected to and controls each of the traffic signal faces 16-22 in a normal manner. Each traffic signal face is illustrated to contain three indications, generally known as red, amber and green. Normally, an incandescent traflic signal lamp and an appropriate colored lens is utilized to establish the color for the indication. In addition, if a mark, such as an arrow to indicate direction, is required, the colored lens is appropriately masked. In trafiic signal face 16, the red indication is generally designated as lamp 30, the amber indication is designated as lamp 32 and the green indication; is designated as lamp 34. Each of the other faces 18-22 has a similar red indication, amber indication and green indication.

In the intersection formed by crossing of highways 12 and 14, the north-south lanes are controlled by traific signal faces 16 and 18. Traffic signal face 16 may be located in the northwest corner of the intersection while traffic signal face 18 may be located in the southeast corner of the intersection. The placement of the trafiic signal faces of FIGURE 1 is merely exemplary and it is contemplatedthat the trafiic signal faces could well be located in other corners of the intersection in accordance with existing traffic signal standards. Typically, traffic signal face 16 located in the northwest corner of the intersection would be used for controlling traflic in the northbound lane of highway 12 while traffic signal face 18 would be used to control trafiic in the southbound lane of highway 12.

Control of traffic flow along one street or highway is generally referred to as traffic movement. The term phase refers to the group of indications used for controlling traffic movement in a programmed sequence. The sequence of traflic movement is the programmed order in which trafiic flow through the intersection is controlled, such as, for example, that vehicles are given the rightof-way to proceed in a given direction, e.g. green indication; are required to stop, e.g. red indication; or are warned of a change in trafiic movement, e.g. amber indication. In FIGURE 1, one phase, which includes trafiic signal faces 16 and 18, controls the traffic movement in both the northbound and southbound directions of highway 12 and a second phase, which includes trafiic signal faces 20 and 22, controls the traffic movement in both the eastbound and westbound directions ofhighway 14. Thus, in FIGURE 1, traffic movement through the intersection is controlled in two phases.

In some intersections, trafiic movement is controlled by lanes or directions thereby requiring phases for each lane or direction. For example, in FIGURE 1 (not shown), trafiic signal faces 16 and 18 and 20 and 22 could be controlled by separate phases such that traffic movement is controlled in four phases.

For purpose of consistency, the use of the terms traffic signal section, indication, indicators or color refers to a traffic signal lamp in combination with a colored lens to form a single light unit which together with other units form a trafiic signal face. In FIGURE 1, this corresponds to the red indication 30 which together with amber indication 32 and green indication 34 forms the trafiic signal face 16. Traffic signal faces 16 and 18 form a single phase as illustrated in FIGURE 1. Thus, the red indications in the tratfic signal faces 16 and 18 are identical indications in the same phase wherein each section is located in a different trafiic signal face.

Use of the term t'raffic signal lamps or indicators in a plurality of traflic signal faces in the same phase includes the indicators used in the same phase for controlling traffic movement. For example, in FIGURE 1, this includes the red, amber and green indications of trafiic signal faces 16 and 18.

In addition, the term trafiic signal lamps or indications in a single traflic signal face includes one or more indication used in a standard traffic signal face. For example, in FIGURE 1, this includes red indication 30, amber indication 32 and green indication 34 in traffic signal face 16.

Traflic signal face 20 is illustrated to be located in the northeast corner of the intersection and is adapted to control the eastbound traffic of highway 14. The trafiic signal face 22 is illustrated herein in the southwest corner of the intersection and is adapted to control the westbound lane of highway 14.

In some installations, it would be possible to install more than one traffic signal face at a given corner of the intersection. For example, the traffic signal face 16 which controls the northbound lane of highway 12 could also have mounted on the same pole in a parallel aligned relationship a traffic signal face (not shown) which is identical to traffic signal face 18 and which would also be used as a second parallel control for the southbound lane of highway 12. A combination of one or more faces in a mountable assembly is generally referred to as a traffic signal head or head. Additionally, other lane control signals or indications could be added to or be a traffic signal face, for example, controlled left and right turn indications, pedestrian control indications and the like.

Trafiic signal faces 16 and 18 serving the northbound and southbound lanes of highway 12 respectively are electrically connected to the traffic signal controller 24 such that all of the red indications, amber indication and green indications would be energized in proper sequence. Similarly, traffic signal faces 20 and 22 would be electrically connected to traffic signal controller 24 in the manner such that the red indication, amber indication and green indication thereof would be energized in proper sequence.

One possible electrical connecting diagram is illustrated in FIGURE 1 for accomplishing the appropriate interconnection between traflic signal faces 16-22 and trafiic signal controller 24. This electrical diagram is believed to be adequately shown by FIGURE 1 and need not be considered in detail here.

Each of the tratfic signal faces 16-22 is illustrated as having a return or neutral of each indication electrically connected to a common neutral. For example, trafiic signal face 16 has the neutrals of its traflic signal lamps in the red indication, amber indication and green indication electrically connected to a common neutral 40. T raffic signal face 18 has the neutrals of all of its traflic signal lamps of each indication electrically connected to a common neutral 42. Traffic signal face 20 has the neutrals of its trafiic signal lamps in each of the indications electrically connected to a common neutral 44. Similarly, traflic signal face 22 has the neutrals of its traffic signal lamps in each of theindications electrically connected to a common neutral 46. The traffic signal controller 24 is electrically connected to and energized from an electrical distribution system, which is generally designated as 48, which may be a volt, 60 cycle, alternating current voltage having a system ground.

Each of the common neutrals 40-46 for trafiic signal faces 1622 respectively is electrically connected to a traffic control system having a control means, generally designated as 52, and a light sensing means, generally designated as 54. The control means 52 includes a unilaterally conducting means such as, for example, a diode 56 having its anode electrically connected to a common neutral bus bar 58. The common neutral bus bar 58 has connecting terminals, generally designated as 60. The connecting terminals 60 have common neutrals 404'6 electrically connected thereto. The cathode of diode 56 is electrically connected via a common neutral 62 back to the system ground of the electrical distribution system 48. The unilaterally conducting means, such as for example diode 56, is effectively electrically connected in series with the signal lamps and is capable of conducting electrical current therethrough through at least a portion of the alternating current cycle.

A switching means such as, for example, a relay 68 having a normally-closed contact 70 and a relay coil 72 is operatively connected to the lamp and the unilaterally conducting means such that the position of the contact 70 controls conduction of the diode 56. This is accomplished by normally-closed contact 70 being electrically connected in parallel to the diode 56. One lead of relay coil 72 is electrically connected to the common neutral 62 while the other lead thereof is electrically connected to the light sensing means 54. When the relay coil 72 is de-energized, normally-closed contact 70 is in a closed position and selectively bypasses or is connected in parallel to the diode 56 and conducts electrical current through the signal lamps of the indicators. When relay coil 72 is energized, the coil 72 causes the normallyclosed contact to be moved to an open position and permits the diode to completely control conduction of the current through the lamps.

In this illustrated intersection of FIGURE 1, the light sensing means 54 includes a photocell 76 which is re sponsive to the background illumination in the vicinity of the intersection. Photocell 76 has one terminal thereof electrically connected via lead 78 to the hot or energized line of the power distribution system 48. The other terminal of the photocell 76 is electrically connected to a relay coil 80 which in turn is connected to the system ground of the electrical distribution system 48. A normally-closed contact 82 controlled by coil 80 is electrically connected before the photocell 76 to the lead 78 and is also connected to a control lead 84. Control lead 84 is in turn connected to the other terminal of relay coil 72 within the control means 52. When the background illumination in the vicinity of the intersection is at a high level, the resistance of photocell 76 is low allowing coil 80 to be actuated holding contact 82 in an open position. When the background illumination decreases below a preselected level, the resistance of the photocell 76 becomes high reducing the voltage across coil 80 thereby deactuating coil 80 which enables contact 82 to move into its normallyclosed position. When contact 82 is in its normally-closed position, relay coil 72 has a voltage applied thereacross from lead 78 causing normally-closed contact 70 to be moved into its open position. When this occurs, the diode 56 is electrically connected in series with each of the signal lamps of the indicators in each of the tralfic signal faces 16-22 thereby abruptly dimming traffic signal lamps connected to the rectifier. By using a rectifier as the diode 56, the power applied to the lamp is decreased to about one-half of its original value and the light intensity drops from about a 100 percent level to about a 26 percent level. The reduction in power and lamp intensity is due to diode 56 conducting only during one-half the portion of the alternating current voltage cycle.

It has been determined that the light responsive dimming circuit disclosed herein must be connected in series with the common neutrals from all of the traffic signal faces in a single phase in order to abruptly and simultaneously dim the traffic signal lamps of that phase from the high intensity level to the predetermined low intensity level. Also, if more than one phase but less than all of the phases are to have the trafiic signal lamps therein abruptly and simultaneously dimmed, the common neutrals from all of the trafiic signal faces in the phases to be dimmed must be connected together and in turn connected in series with the light responsive dimming circuit.

Similarly, if all of the trafiic signal lamps of all of the phases of the entire intersection are to be abruptly and simultaneously dimmed between the high intensity level and the predetermined low intensity level, all of the common neutrals from all of the trafiic signal faces must be connected together and in turn connected in series with the light responsive dimming circuit disclosed herein.

If the light responsive dimming circuit disclosed herein is connected in series with only some of the common neutrals of a single phase to be dimmed or with only some of the common neutrals of different phases, a ground loop current is established such that the desired dimming cannot be obtained. When this occurs, all of the traflic signal lamps at the entire intersection are slightly dimmed to somewhere between the high intensity level and the predetermined low intensity level. It appears that other ground loop current paths occur when the light responsive dimming circuit is connected to only some common neutrals in that the unenergized lamp filaments ofier a return path having a lower resistance than the dimming circuit.

In summary, the light responsive dimming circuit and system, as disclosed, when properly connected such that unwanted ground loop current paths are not established, provides the desired dimming.

In certain applications, it is desirable not to abruptly and simultaneously dim either one phase or the entire intersection but to proportionally dim only selected trafiic signal lamps between the high intensity level and the predetermined low intensity level in response to sensed background illumination. Such a light responsive electrical lamp dimming system is disclosed and claimed in an application filed concurrently herewith of Stanley L. Ross and Joseph T. Fitzpatrick, identified as Ser. No. 742,627.

FIGURE 2 is a schematic diagram of another circuit 52' which can be used in place of the light responsive electrical lamp dimming circuit 52 of FIGURE 1. Circuit 52 includes a terminal connecting means such as, for example, two ground connecting strips 88 and 90 which have a plurality of apertures 92 which are adapted to receive the common neutral from each traffic signal face. The common neutrals are held securely in place by means of fasteners 94. The circuit 52' includes a switching means, generally designated as 98. The switching means in this embodiment is a relay means which includes a control means, such as for example contact means, which in this example is a pair of movable contacts 102 and 104. Each of the contacts 102 and 104 when in its normally-closed position is electrically connected to fixed contacts 106 and 108 respectively. Movable contact 102 is electrically connected to a relay grounding terminal 112, which terminal is electrically connected to system ground 114. The fixed contact 106 is connected to a terminal contact 116.

Movable contact 104 is electrically connected to a relay grounding terminal 120, which terminal is in turn connected to system ground 114. Fixed contact 108 is electrically connected to a terminal contact 122.

The relay means 98 also includes an actuating means such as, for example, relay coil 126. Relay coil 126 is mechanically connected to the movable contacts 102 and 104. When coil 126 is energized, the normally-closed movable contacts 102 and 104 are moved into an open position.

The ground connecting strip 88 is electrically connected via a conductor 130 to terminal contact 116. A unilaterally conducting means such as, for example, a rectifier or diode 132 has its cathode electrically connected to the terminal contact 116 and its anode electrically connected to the relay grounding terminal 112. It is readily apparent that when movable contact 102 is in its normally-closed position contacting fixed contact 106, diode 132 is shorted out or bypassed. However, when movable contact 102 is moved into its open position, diode 132 is electrically connected between the ground connecting strip 88 and system ground 114. When this occurs, the diode 132 is rendered conductive during only substantially one-half of the alternating current voltage cycle. In the preferred embodiment, the alternating current source is a 120 volt, 60 cycle, alternating current voltage suchthat only a half cycle voltage wave is applied across the traific signal lamp. Thus, the voltage applied to the trafiic signal lamp is reduced to substantially one-half thereby reducing the intensity of the traffic signal lamps.

Ground connecting strip 90 is electrically connected via a conductor 136 to terminal contact 122. A second unilaterally conducting means or diode 138 has its cathode electrically connected to terminal contact 122 and its anode connected to relay grounding terminal 120'. When movable contact 104 is moved between its normallyclosed position and open position, the conduction of the diode 138 is identical to that set forth with respect to the operation of diode 132. Each of the diodes 132 and 138 is mounted on a heat sink or aluminum plate 140. The heat sink 140 dissipates the heat generated within the diodes 132 and 138 when the movable contacts 102 and 104 are in their open positions rendering diodes 132 and 138 conductive.

A photocell 142 is electrically connected to the alternating current source 144 and to the relay coil 126. When the illumination in the vicinity of the photocell decreases below a preselected level, the photocell 1 42 applies the alternating current voltage from source 144 across relay coil 126. When relay coil 126 is so energized, the movable contacts 102 and 104 are moved from their normally closed positions to their open positions thereby connecting diodes 132 and 138 into the ground circuit portion of the trafiic signal sections. Thus, photocell 142 functions substantially as a static switch to abruptly dim the lamps from full intensity to a reduced intensity when the background illumination in the vicinity of the intersection drops below the predetermined operating level 'of the photocell 142.

Typical components which can be utilized for practicing the circuit of FIGURE 2 are set forth hereinbelow:

.Relay means 98-Potter & Brumfield #PRl I EY-DPDT Rectifiers 132, 138Westinghouse #IN1186A Photocell 142-Fisher Pierce photocell relay #6600A Heat sink 140-Thermalloy type #6123 T It is understood that other modifications, improvements and equivalents thereof can be made to the embodiments disclosed herein of the light responsive electrical lamp dimming system disclosed herein. All such modifications, improvements, equivalents and the like are deemed to be within the scope of the appended claims.

What is claimed is:

1. A light responsive traffic signal lamp dimming circuit adapted for use with a trafiic signal controller energized from an electrical distribution system having a system ground, said dimming circuit being adapted to be connected to common neutrals of all of the traffic signal faces in each phase in which trafiic signal lamps are to be dimmed, said dimming circuit being adapted to abruptly and simultaneously dim said traflic signal lamps from a high intensity level when the sensed background illumination is above a preselected level and to a predetermined low intensity level when the sensed background illumination is less than the preselected level, said circuit comprising a unilaterally conducting means adapted to be electrically connected between said common neutrals of said traflic signal faces and said system ground and in a direction to be conductive for approximately one-half of the alternating current voltage cycle; a switching means including a switchable circuit device having a first conduction state and a second conduction state electrically connected in parallel to said unilaterally conducting means, said switchable circuit device when in said first conduction state being capable of bypassing said unilaterally conducting means for connectingsaid lamps across said alternating current-voltage source to operate said lamps at said high intensity level and when in said second conduction state being capable of enabling said unilaterally conducting means to be rendered conductive for connecting said lamps across said alternating current voltage source for approximately one-half of the alternating current voltage cycle to operate said lamps at said predetermined low intensity level, and

control means having a first control state and a second control state operatively connected to said switchable circuit device for changing said switchable circuit device from said first conduction state to said second conduction state, said control means when in said first control state causing said switchable circuit device to be in said first conduction state and when in said second control state causing said switchable circuit device to change from said first conduction state to said second conduction state; and

light sensing means electrically connected to said control means for sensing background illumination and for changing said control means from said first control state to said second control state when said sensed background illumination is less than said preselected level to change said switching circuit device from said first conduction state to said second conduction state to abruptly and simultaneously change the intensity level of said lamps in said traffic signal faces of said at least one phase from said high intensity level to said low intensity level while said sensed background illumination is less than said preselected level.

2. The light responsive dimming circuit of claim 1 wherein said unilaterally conducting means is a rectifier, said switching means is a relay, said switchable circuit device is at least one contact having a normally-closed position which corresponds to said first conduction state and an open position which corresponds to said second conduction state, said control means is a coil and said light sensing means is a photocell which energizes said coil to move said at least one contact from said normallyclosed position to said open position when the sensed background illumination is less than said preselected level.

3. The light responsive dimming circuit of claim 2 further comprising a ground connecting strip having a plurality of openings which are adapted to receive said common neutrals from said traffic signal faces, said ground connecting strip being electrically connected to the cathode of said diode.

4. A light responsive trafiic signal lamp dimming system adapted for use with an intersection traffic signalling system to abruptly and simultaneously dim trafiic signal lamps of at least one phase between a high intensity level and a predetermined low intensity level in response to changes in background illumination in the vicinity of the intersection, said traffic signalling system including a traffic signal controller which is energized from an electrical distribution system having a system ground and which selectively energizes, in a predetermined sequence, said trafiic signal lamps in all of the trafiic signal faces in said phase and wherein said traific signal faces each have a single common neutral which is electrically connected to the trafiic signal lamps located therein, said system comprising ground connecting means adapted to be electrically connected to each of said common neutrals from the traffic signal face;

unilaterally conducting means electrically connected between said ground connecting means and adapted to be connected to said system ground in a direction to enable said unilaterally conducting means to be conductive when said system ground is at a higher potential than said ground connecting means;

relay means including contact means having a first position and a second position electrically connected in parallel to said unilaterally conducting means and capable of bypassing said unilaterally conducting means when said contact means are in said first position and capable of enabling said unilaterally conducting means to be conductive when said contact means are in said second position, and

relay actuating means operatively connected to said contact means for selectively moving said contact means between said first position and said second position; and

a light responsive means electrically connected to and controlling said relay actuating means for moving said contact means to said first position when the sensed background illumination in the vicinity of said intersection is at an illumination level which exceeds a preselected level and for controlling said relay actuating means to move said contact means to said second position when said sensed background illumination is less than said preselected level;

said unilaterally conducting means being responsive to said contact means being moved from said first position to said second position by being conductive for substantially one-half of an alternating current voltage cycle to concurrently apply a reduced voltage to said traffic signal lamps in said traflic signal faces of said at least one phase resulting in all of said traffic signal lamps in said at least one phase being abruptly and simultaneously dimmed to a predetermined low intensity level.

5. The light responsive trafiic signal lamp dimming system of claim 4 wherein all of the common neutrals of all of the trafiic signal faces of all the phases are connected to said ground connecting means enabling said system to abruptly and simultaneously dim all of the traffic signal lamps of the entire intersection between said high intensity level and said predetermined low intensity level as a function of sensed background illumination.

6. The light responsive traflic signal lamp dimming system of claim 4 wherein said ground connecting means includes a first and a second ground connecting strip each of which contains a plurality of openings adapted to receive said common neutrals from each of said trafiic signal faces, wherein said unilaterally conducting means includes a first diode and a second diode with the cathodes thereof being electrically connected to said first and second ground connecting strips respectively and wherein said contact means includes a first and a second contact electrically connected in parallel to said first and second diodes respectively.

7. A light responsive trafiic signal dimming apparatus adapted for use with a trafiic signal controller having a grounding terminal for selectively dimming all of the trafiic signal lamps in all of the trafiic signal faces in at least one phase at an intersection from a high intensity level to a predetermined low intensity level when the sensed background illumination is less than a preselected level, said apparatus comprising first and second ground connecting strips each of which has a plurality of openings adapted to be electrically connected to a common neutral from each of said traffic signal faces of said at least ohe phase;

first and second diodes having the cathodes thereof electrica y connected to said first and second ground connecting strips respectively and the anodes thereof electrically connected to a common grounding neutral which is adapted to be connected to said grounding terminal;

a relay having a relay coil and first and second normally-closed contacts, said first and second normallyclosed contacts being operatively connected across said first and second diodes respectively and said common grounding neutral;

a photocell operatively connected to said relay coil and adapted to be energized from the power source energizing said traffic signal controller, said photocell being adapted to be responsive to said sensed background illumination being less than said preselected level to energize said relay coil from said power source to move said first and second normallyclosed contacts to their open positions enabling said first and second diodes to be rendered conductive to abruptly and simultaneously reduce the intensity of all of said trafiic signal lamps in said trafiic signal faces in said at least one phase from said high intensity level to said predetermined low intensity level while said sensed background illumination is less than said preselected level and to de-energize said relay coil to permit said first and second normally-closed contacts to close bypassing said first.and second diodes to increase the intensity of said traffic signal lamps from said predetermined low intensity level to said high intensity level while said sensed background illumination is above said preselected level.

8. A light responsive electrical lamp dimming circuit adapted for use with a lamp switching means to abruptly and simultaneously dim all of the lamps connected in parallel in one switching circuit across an alternating current source and system ground wherein the switching circuit is controlled by said switching means to concurrently energize all of the lamps in the same switching circuit, said lamps in said switching circuit being electrically connected to a single common neutral normally connected to said system ground, said circuit comprising ground connecting means adapted to be electrically connected to said common neutral from said lamp switching circuit;

unilaterally conducting means electrically connected between said ground connecting means and adapted to be connected to said system ground in a direction to enable said unilaterally conducting means to be conductive when said system ground is at a higher potential than said ground connecting means;

relay means including contact means having a first position and a second position electrically connected in parallel to said unilaterally conducting means and capable of bypassing said unilaterally conducting means when said contact means are in said first position and capable of enabling said unilaterally conducting means to be conductive when said contact means are in said second position, and

relay actuating means operatively connected to said contact means for selectively moving said contact means between said first position and said second position; and

a light responsive means electrically connected to and controlling said relay actuating means for moving said contact means to said first position when the sensed background illumination in the vicinity of said lamps is at an illumination level which exceeds a preselected level and for controlling said relay actuating means to move said contact means to said second position when said sensed background illumination is less than said preselected level,

said unilaterally conducting means being responsive to said contact means being moved from said first position to said second position by being conductive 13 for substantially one-half of an alternating current voltage cycle to concurrently appl a reduced voltage to said lamps energized by said switching circuit resulting in all of said energized lamps being abruptly and simultaneously dimmed to a predetermined low 5 intensity level.

References Cited UNITED STATES PATENTS 14 3,263,932 8/ 1966 Pettersson 315-292 3,283,297 11/1966 Pfenninghousen et a1. 34Q 22 3,416,032 12/1968 Johns et a1. 315-149 JOHN W. HUCKERT, Primary Examiner SIMON BRODER, Assistant Examiner US. Cl. X.R. 

